There are numerous applications in existing devices for light projecting and light receptive optical systems wherein it is desirable to maintain the power or quality of a beam of light. According to conventional optical systems, light beams must be processed by off-axis optics to eliminate both supporting structure and other obscurations. Off-axis optics with the requirement for asymetrical optical elements, necessarily increase the size of the system since the beam is deflected from the original axis. Additionally, in order to maintain adequate beam quality, specially designed, complex, high precision, optical components must be employed, substantially increasing the cost of the optical system. Direct expansion done in a coaxial system requires optical components to be on-axis. This means that the necessary supporting structure for the optical components must pass through the beam, thereby reducing the total power delivered. Where the supporting structure can be eliminated from the beam, such as the Coude-Coelostat, a portion of the beam is reflected back in its original direction thus losing power. This is undesirable. The term "optical structure" as used hereinafter is intended to include optical components and supporting structure that would normally block or obscure part of the beam power.
Therefore, it is desirable to have an optical system capable of producing a non-annular beam, that transmits the full beam power without off-axis optics, or other expensive optical elements. Such a system is particularly desirable where reflected back beams would degrade system performance.